I was playing around in my room and slipped and hit my dresser with the inside of my ankle it bruised and it hurts when u tounch it. why ?

Because you : Injured it....there are nerve endings that were injured, a swelling response likely occured....it's no different then if your punched in the arm...this hurts also...

Ankle Bruise: it hurts because you injured the tissue enough to cause it to bleed which causes the bruise. In medical terms we call a bruise a hematoma, which is blood in the tissues.